In an analysis using a liquid chromatograph, an auto-sampler is used to automatically introduce a plurality of liquid samples to the column in a predetermined order. One commonly known type of auto-sampler uses a so-called total volume injection method, in which a predetermined amount of sample is collected from a sample bottle and the entire amount of the collected sample is injected into a passage through which a mobile phase is flowing (see Patent Document 1).
In a sample injection process by the total volume injection method, a predetermined amount of sample is suctioned from a sample bottle through a sampling needle and sent into a sample loop (measuring loop) connected to the rear end of the sampling needle. Subsequently, the tip of the sampling needle is connected to a sample injection port, after which a six-way valve located ahead of the sample injection port is operated to create a flow passage which serially connects the mobile phase container, the sample loop, the sampling needle, the sample injection port, the six-way valve and the column in this order. Then, a mobile phase in the mobile phase container is pumped into the flow passage by means of a liquid supply pump, whereby the sample held in the sample loop is flushed away, to be entirely introduced into the column.
In the auto-sampler using the total volume injection method, a high pressure is applied to the mobile phase to shorten the staying time of the sample in the column and thereby reduce the analyzing time. For this purpose, it is necessary to sufficiently seal the connection part of the passage so that it can withstand the high pressure. Particularly, in the sample injection port, it is naturally important to achieve a high level of sealing effect at the connection part of the sampling needle, i.e. the contact area between the sampling needle and a resin-made sealing member having a through-hole communicating with the needle. Furthermore, the sealing on the opposite side of the sealing member, i.e. on the contact surface between the sealing member and a metallic housing having a sample introduction hole communicating with the through-hole of the sealing member, is also important.
FIG. 5 shows a schematic configuration of a conventional sample injection port 50. A resin-made seal member 51 having a through-hole 511 for allowing the passage of a sample is held in a cavity of a metallic housing 52, on which a cap 53 is placed to apply a pressure to the upper side of the seal member 51. This pressure makes the lower surface of the seal member 51 tightly pressed on the bottom surface of the cavity of the housing 52, thus maintaining the sealing effect at the connection between the through-hole 511 of the sealing member 51 and the sample introduction hole 521 of the housing 52.
As shown in FIG. 6, the housing 52 may have a ring-shaped projection 522 formed around the opening of the sample injection hole 521 at the bottom of the cavity. In this case, the lower surface of the sealing member 51 comes in contact with only the upper surface of the projection 522. Since the contact area is smaller, a higher pressure can be applied to the contact surface, whereby the sealing effect at the connection part of the passage can be improved.